This invention relates to composite core members and aluminum conductor composite core (ACCC) reinforced cable products made therefrom. This invention further relates to a forming process for an aluminum conductor composite core reinforced cable (ACCC). In the traditional aluminum conductor steel reinforced cable (ACSR) the aluminum conductor transmits the power and the steel core is designed to carry the transfer load.
In an ACCC cable, the steel core of the ACSR cable is replaced by a composite core comprising at least one reinforced fiber type in a thermosetting resin matrix. Replacing the steel core has many advantages. An ACCC cable can maintain operating temperatures in the range of about 90 to about 230° C. without corresponding sag induced in traditional ACSR cables. Moreover, to increase ampacity, an ACCC cable couples a higher modulus of elasticity with a lower coefficient of thermal expansion.
This invention relates to an aluminum conductor composite core reinforced cable suitable for operation at high operating temperatures without being limited by current operating limitations inherent in other cables for providing electrical power wherein provision of electrical power includes both distribution and transmission cables. Typical ACSR cables can be operated at temperatures up to 100° C. on a continuous basis without any significant change in the conductor's physical properties related to a reduction in tensile strength. These temperature limits constrain the thermal rating of a typical 230-kV line, strung with 795 kcmil ACSR “Drake” conductor, to about 400 MVA, corresponding to a current of 1000 A.
Conductor cables are constrained by the inherent physical characteristics of the components that limit ampacity. More specifically, the ampacity is a measure of the ability to send power through the cable wherein increased power causes an increase in the conductor's operating temperature. Excessive heat causes the cable to sag below permissible levels. Therefore, to increase the load carrying capacity of transmission cables, the cable itself must be designed using components having inherent properties that withstand increased ampacity without inducing excessive sag.
Although ampacity gains can be obtained by increasing the conductor area that wraps the core of the transmission cable, increasing conductor weight increases the weight of the cable and contributes to sag. Moreover, the increased weight requires the cable to use increased tension in the cable support infrastructure. Such large load increases typically would require structure reinforcement or replacement, wherein such infrastructure modifications are typically not financially feasible. Thus, there is financial motivation to increase the load capacity on electrical transmission cables while using the existing transmission liens.
European Patent Application No. EP1168374A3 discloses a composite core comprised of a single type of reinforced glass fiber and thermoplastic resin. The object is to provide an electrical transmission cable which utilizes a reinforced plastic composite core as a load bearing element in the cable and to provide a method of carrying electrical current through an electrical transmission cable which utilizes an inner reinforced plastic core. The composite core fails in these objectives. A one fiber system comprising glass fiber does have the required stiffness to attract transfer load and keep the cable from sagging. Secondly, a composite core comprising glass fiber and thermoplastic resin does not meet the operating temperatures required for increased ampacity, namely, between 90 and 230° C.
Composite cores designed using a carbon epoxy composite core also have inherent difficulties. The carbon epoxy core has very limited flexibility and is cost prohibitive. The cable product having a carbon epoxy core does not have sufficient flexibility to permit winding and transport. Moreover, the cost for carbon fibers are expensive compared to other available fibers. The cost for carbon fibers is in the range of $5 to $37 per pound compared to glass fibers in the range of $0.36 to $1.20 per pound. Accordingly, a composite core constructed of only carbon fibers is not financially feasible.
Physical properties of composite cores are further limited by processing methods. Previous processing methods cannot achieve a high fiber/resin ratio by volume or weight. These processes do not allow for creation of a fiber rich core that will achieve the strength to compete with a steel core. Moreover, the processing speed of previous processing methods are limited by inherent characteristics of the process itself. For example, traditional pultrusion dies are approximately 36 inches, having a constant cross section. The result is increased friction between the composite and the die slowing processing time. The processing times in such systems for epoxy resins range within about 6 inches/minute to about 12 inches/minute, which is not economically feasible. Moreover, these processes do not allow for composite configuration and tuning during the process, wherein tuning comprises changing the fiber/resin ratio.
It is therefore desirable to design economically feasible ACCC cables having at least one reinforced fiber type in a thermosetting resin matrix comprising inherent physical characteristics that facilitate increased ampacity without corresponding cable sag. It is further desirable to process composite cores using a process that allows configuration and tuning of the composite cores during processing and allows for processing at speeds in the range of about 9 ft/min to 50 ft/min.